US2220792A

US2220792A - Composition and process for preparing cast iron products

Info

Publication number: US2220792A
Application number: US315089A
Authority: US
Inventors: William D Moore
Original assignee: American Cast Iron Pipe Co
Current assignee: American Cast Iron Pipe Co
Priority date: 1940-01-22
Filing date: 1940-01-22
Publication date: 1940-11-05
Anticipated expiration: 1957-11-05

Description

iatented Nov. 5, 1946 U Ni PAT lE CGDHGSITION AND PROCESS FOR PREPAR- IN G (EAST IRON PRODUCTS No Drawing. Application January 22, 1940,

Serial No. 315,089

12 Claims.

This invention relates to the production of iron castings, and has particular utility in the preparation of cast iron products such as blanks'for bolts, nuts, glands, keys, fittings, etc., for use with cast iron piping, although as will be apparent to those skilled in the art it has wider utility. However, the invention will be exemplified by its application to the production of accessories for cast iron'pipes.

In producing cast iron fittings for use with cast iron pipes it is of major importance that such accessories, which frequently project from the piping at the joints, and aretherefore subject not only to soil corrosion but also to stray current electrolysis because of.stray currents leaving the pipe line at such projections, be not only corrosion resistant but also cathodic with respect to the metal of the line.

It is an object of this invention to produce castings which in the case of accessories for cast iron pipes will obviate the difliculties heretofore experienced with cast iron accessories, such as bolts and glands, corroding more rapidly than the piping with which they are associated, and therefore to produce accessories that are resistant not only to normal corrosion and soil corrosion but also to corrosion due to stray current electrolysis;

In the commercial production of accessories for cast iron pipes it is important that the cost of production be reduced to a minimum. This involves not only low cost operations in the actual casting of the accessory parts or blanks-and in my copending application filed concurrently herewith and entitled Method and apparatus for making small castings I have disclosed and claimed an improved method and apparatus for casting bolts or the like to'take advantage of the present invention in the production of such accessories-but also a composition and procedure such that the costs of preparing the metal for casting and the costs for preparing the castings for use are, by reason of equipment, time, labor, etc., involved, also reduced to a minimum.

It isa further object of this invention to provide a composition and procedure for producing castings which meet the foregoing requirements and which therefore permit the metal to be prepared for casting with relatively inexpensive equipment, because of lower melting temperatures, which decrease the costs involved in the melting operation, because of decrease in time and labor costs, and which materially reduce the costs of treatment'of the cast iron blanks in preparing them for use because of large savings in time and labor costs therein involved.

It has heretofore been proposed, as in the patent of Williams and Boegehold, No. 1,591,598, granted July 6, 1926, to produce a casting which has a white iron fracture by rapidly chilling, at a rate to prevent graphite precipitation in flake" form, an iron which is relatively highin silicon, and then annealing the same at a temperature of about 1500 to 1700" F. over a period, preferably for about four hours and not. exceeding fifteen hours,-.

to convert the cementite into temper carbon and ferrite in order to malleableize the iron. While this composition and procedure may-be desirable for some purposes the exigencies incident to other purposes, as the use of cast iron accessories for cast iron pipes, for example, make it important that the castings be possessed of characteristics not obtained through use of such a composition after which it is reheated to a temperature be tween 1250 to 1300 F., preferably 1270 F., for

from ten to thirty-five hours, to break down the pearlite into ferrite and graphite, and then it is further heated at a temperature between 1325 and 1360 F., for two and one half to seven and one half hours to cause a redistribution of the carbon particles. Again, while productive of castings having desirable characteristics for certain purposes, the procedure here involved is high in time consumption and the resulting castings lack highly desirable characteristics to fit them for certain uses, as theuses'to which cast iron pipe accessories are put,'for example.

It is a further object of this invention to overcome the disadvantages of these heretofore proposed compositions and procedures and to pro-- vide a composition and process for producing castings which enable the same to be more economically produced and also given those characteristics which render them particularly suitable for other uses such as referred to.

Another object of this invention is to provide a. composition and process for making castings which are efiective in producing important economies in the melting, casting and annealing procedures.

Another object of this invention is to provide a composition and process of the type characterized which gives high metal strength.

Another object of this invention is to provide a composition and process of the type character ized which gives the desired elastic properties.

Another object of this invention is to produce a composition and process of the type characterized which produces a metal that is easily machined.

tially uniform in their characteristics and properties.

Another object of this invention is to provide a composition and process of the type characterized which enables more uniform castings to be produced notwithstanding there may be a wider range in the composition of different castings.

Another object of this invention is to produce a composition and process of the type characterized which produces substantially uniform high test castings from cupola melted metal.

Another object of this invention is to provide a composition and process of the: type characterized which facilitates production of castings at relatively high speed in automatic or semiautomatic machines.

Another object of this invention is to produce a composition and process of the type characterized which enables the annealing time to be greatly reduced.

Another object of this invention is to provid a composition and process of the type characterized which produces castings that are highly resistant to corrosion.

Another object of this invention is to provide a composition and process of the type characterized which produces castings that in corrosive soils are cathodic to iron articles with which they are used.

Other objects will appear as the description of the invention proceeds.

Referring now more particularly to the production of accessories for cast iron pipes, it is highly desirable that the castings possess a relatively high tensile strength, which should be at least 60,000 pounds per square inch. As, these castings must ordinarily be machined, as in threading, for example, the hardness of the castings should be low enough to permit such machining, and a hardness value of 95 Rockwell "13 is found to be a satisfactory maximum limit. Particularly in the production of bolts, or other elements that may be in tension when in service. it is desirable that the elastic properties of the metal be such that the metal can not be left in a stretched condition, 1. e., bolts on tightening with a wrench should not be under a stress that is higher than the yield point, but should possess such stifiness as will give a brittle break; this is found to be satisfied if the ultimate elongation does not exceed on the order of 5%.

The foregoing characteristics as well as other desired characteristics and properties hereinbefore referred to are obtained by the use of the composition and procedure now to be described.

In accordance with the present invention the preferred composition of the metal to be cast is:

Copper 0.75 to 1.25 The remainder iron except for such impurities as may exist in iron commonly used in castings.

The foregoing composition possesses the advantage that it has a lower freezing point than iron commonly used for malleable castings, and

therefore may be easily melted in a cupola with sufficient temperature and control of molten meta1 and the economies incident to the use of such equipment.

The foregoing metal is cast in a mold having a materially higher rate of heat conduction than the commonly used green sand mold. While various materials as graphite, silicon carbide, steel, etc., may be employed, the preferred mold material is cast iron. Whatever the material used the mold is such that the iron ascast will have a relatively high rate of cooling so that nearly all of the constituent carbon is in the forni of combined carbon and the metal at least in sections of a square inch or less will have an all-white fracture. Rapid cooling also effects economies in the higher rate of production rendred available.

The castings are then subjected to an annealing cycle. According to the preferred cycle the castings are raised to a temperature of at least 1750 F., preferably 1800 F., in a period on the order of sixty minutes, and maintained at said temperature for at least thirty minutes, preferably one hour. This is followed by air-cooling to a temperature on the order of about 1200 F., in a period on the order of twenty to thirty minutes, whereupon the castings are reheated, in a period on the order of thirty to fifty minutes, to a temperature of at least 1400 F., preferably 1450 F., and maintained at that temperature for at least thirty minutes, preferably forty-five minutes. Then the castings are furnace cooled to approximately 1000 F. in a period on the order of about twenty minutes, and then air-cooled to atmospheric temperature, which may involve a period on the order of from thirty to fifty minutes.

The resulting metal is similar in many respects to malleable or pearlitic malleable iron, but differs therefrom in composition in that its silicon content is materially higher, and its copper content effects certain important functional advantages.

The composition, the casting procedure and the heat treatment herein described are closely interrelated and adapted to each other in order to secure the results desired, that is if the composition described is used and cast as described and then subjected to the heat treatment described, the desired results are obtained to a higher degree than if a different composition or a different method of casting or a different heat treatment is used.

The use of a relatively high silicon content causes the combined carbon of the as-cast casting to break down rapidly, in whole or in part, so that the annealing period is materially decreased and yet the resulting product is capable of ,being freely machined. At the same time the presence of a relatively large amount of silicon causes a strengthening and hardening of the ferrite constituent so that though nearly all of the combined carbon be reduced to graphitic form the casting will still be strong and sufliciently hard to provide the desired characteristics hereinbefore referred to.

The presence of the copper not only renders the iron resistant to corrosion, including soil corrosion, but also renders the casting cathodic with respect to the cast iron parts with which it is associated, so as largely if not entirely to offset the more rapid corrosion from stray current electrolysis that has heretofore been experienced where projecting cast -iron elements are associated with cast iron pipes or the like. The presence of copper also increases the machinability and gives greater strength for a given hardness.

Therefore, with the composition ranges as hereinabove disclosed annealing to the point where practically all the combined carbon is reduced to graphitic carbon is not critical, as the casting may possess the desired properties of strength, elasticity, and machinability even though there be combined carbon in the annealed casting up to a maximum of 0.60% carbon. Within this range the effect of increasing combined carbon renders the casting stronger, harder and more brittle, and yet the casting is possessed of the required machinability.

Furthermore, the use of the annealing cycle disclosed, in conjunction with the composition disclosed, results in the finished castings having substantially uniform characteristics even though -the silicon content as between different castings be substantially different, as long as the silicon content is within the desired range heretofore disclosed. For example, if one casting has the minimum permitted silicon content, i. ,e., 2.50%, the annealing cycle will not completely break down the combined carbon present in the casting as cast, and the combined carbon remaining will provide the desired strength, hardness, and elastic properties, while the metal is still tough and machinable; if another casting has the maximum silicon content, i. e., 4.0%, the same annealing cycle will almost completely break downthe combined carbon, but the presence of the larger amount of silicon in the ferrite matrix will produce substantially the same strength, hardness and elastic properties as the other casting, and the metal will be of substantially the same toughness and machinability. Similarly, when a casting having a silicon content anywherebetween the limits heretofore stated is subjected to the same annealing cycle, the combined carbon will be reduced to an amount depending largely upon the amount of silicon, so that uniform properties in the annealed casting are obtained even with wide variation of silicon content.

It will therefore be perceived that by the present invention a composition and procedure for producing castings, for example, cast iron accessories for cast iron pipes, has been provided whereby the castings possess the characteristics and properties heretofore pointed out. The presence of the copper renders the castings highly resistant to corrosion and as the metal so cast is cathodic with respect to the cast iron pipes when used therewith, corrosion from stray current electrolysis is at least reduced to that point whereby the accessories are substantially as dur-' able as the cast pipe itself. The presence of the relatively high percentage of silicon results in a. lowering of the freezing point so that the melt can be effected with suflicient temperature and control in a cupola, which is ordinarily the most economical method of melting iron. B rapidly chilling thecasting nearly all of the carbon is in the form of combined carbon, so that the characteristic white fracture exists in the casting as cast, particularly for sections not exceeding about one square inch, and finer grain is also attained. The cementite of the as-cast casting may then be economically changed to a suflicient amount by reason of the aforesaid annealing procedure to provide a casting of the desired characteristics, the presence of the high percentage of silicon making it unnecessary that all of the combined carbon be changed to graphitic carbon because the silicon function complementarily to the extent to which combined carbon is reduced, so that substantially uniform properties are obtained though the silicon content be varied within the specified limits.

At the same time a casting of the composition and treatment before described provides a tensile strength in excess of 60,000 pounds per square inch, a hardness not exceeding 95 Rockwell B, and a stiffness that provides a brittle break with an elongation that does not exceed approximately Also the casting may be readily machined, to provide threads in the case of bolts for example, etc. The lower freezing temperature, enabling the melt to be effected in a cupola, the shortened casting time with use of permanent molds, and the shortened and simplified annealing time and procedure involved in the present invention are productive of important economies while the resulting metal is possessed of those characteristics which particularly suit it for use in accessories for cast iron piping.

While the preferred procedure of the present invention has been described with considerable particularity it is to be expressly understood that the invention is not to be restricted thereto. Variations in the temperature used in both stages of annealing may be made, as before pointed out, as may also variations in the times used, the preferred procedure for both economy of production and resulting metal properties and characteristics having been given but with the recognition that variations may be made in both times and temperatures, depending in part on the characteristics desired in the annealed metal, its constitution, the importanceof the time relationship to provisions for heating the castings, and other factors that will be apparent to those skilled in the art; variations may also be made in the constituents of the metal within the limits specified; while the foregoing composition and annealing cycle are those which have been found to be of particular utility in the production of cast iron bolts and the like, the invention is of wider utility in the production of other castings, in which case some variation in the carbon and silicon content and in the annealing cycle may be advantageous and will be Within the broader aspects of this invention, as its principles have been explained above, all as will be apparent to those skilled in the art. While the composition, the casting procedure and the annealing procedure are closely interrelated and when used together are best calculated to give the desired results, improvement has been effected over prior procedures if the annealing procedure of.-the present invention be followed though using other suitable compositions and/or casting procedures or the composition of the present invention be used though using other suitable casting and/or annealing procedures. Reference ,is therefore to be had to the appended claims for a definition of the present invention.

What is claimed isz 1. As a new article of manufacture, heat treated white cast iron containing from about 2.50% to 4.00% silicon, 2.00% to 2.60% carbon, 0.60% to 1.00% manganese, 0.75% to 1.25% copper, and less than 0.13% sulfur and 0.10% phosphorus.

2. The process of making malleable iron castings which includes melting an iron mixture containing from about 2.50% to 4.00% silicon, 2.00% to 2.60% carbon, 0.60% to 1.00% manganese and 0.75% to 1.25% copper, pouring the iron melt into a mold of sufllciently high heat conductivity to chill the casting so rapidly, that nearly all of the carbon is combined carbon, and then annealing the casting.

3. The process of making malleable iron castings which includes melting an iron mixture containing from about 2.50% to 4.00% silicon and from 0.75% to 1.25% copper, then annealing the casting at a temperature in excess of 1750 F. for more than thirty minutes, then air-cooling the casting to a temperature not exceeding about 1200 F., then reheating the casting to a temperature in excess of 1400 F. and maintaining the same thereat for more than thirty minutes, and then again cooling the casting.

4. The process of making malleable iron castings which consists in making a white iron casting from an iron mixture containing from about 2.50% to 4.00% silicon and from 0.75% to 1.25% copper, pouring the melted metal into a mold of sufficiently high heat conductivity to chill the casting so rapidly that nearly all of the carbon is in the form of combined carbon, and then annealing the casting at a temperature in excess of 1750 F. for more than thirty minutes, then air-cooling the casting to a temperature, not exceeding about 1200 F., then reheating the casting to a temperature in excess of 1400 F. and maintaining the same thereat for more than thirty minutes, and then again cooling the casting.

5. The process of making malleable iron castings which includes melting an iron mixture containing from about 2.50% to 4.00% silicon and from 0.75% to 1.25% copper, then annealing the casting at a temperature of approximately 1800 F. for approximately one hour, air-cooling the casting to a temperature not exceeding about 1200 F., further annealing 'the casting at approximately 1450 F. for approximately threequarters of an hour, and again cooling the casting.

6. The process of making malleable iron castings which includes melting an iron mixture containing from about 2.50% to 4.00% silicon and from 0.75% to 1.25% copper, pouring the melted metal into a mold of sufllciently high heat conductivity to chill the casting so rapidly that nearly all of the carbon is in the form of combined carbon, then annealing the casting at a temperature of approximately 1800 F. for approximately one hour, then air-cooling the casting to a temperature not exceeding about 1200 F., further annealing the casting at approximately 1450 F. for approximately three-quarters of an hour, and then again cooling the casting.

7. The process of making malleable iron castings which includes melting an iron mixture containing from about 2.50% to 4.00% silicon, from about 2.00% to 2.60% carbon and from about 0.60% to 1.00% manganese casting the iron into a mold of sufflciently high heat conductivity to chill the casting so rapidly that nearly all the contained carbon is in the form of combined carbon, annealing the casting at a temperature in excess of 1750 F. for a timein excess of thirty minutes, air-cooling the casting to a temperature not exceeding about 1200 F., again annealing the casting at a temperature in excess of 1400 F. for a period in excess of thirty minutes, and again cooling the casting.

8. The process of 'making malleable iron castings which includes melting an iron mixture containing from about 2.50% to 4.00% silicon, from about 2.00% to 2.60% carbon and from about 0.60% to 1.00% manganese, casting the iron into a mold of suillciently high heat conductivity to chill the casting so rapidly that nearly all the contained carbon is in the form of combined carbon, annealing the casting at approximately 1800 F. for approximately one hour, air-cooling the casting to a temperature not exceeding about 1200" F., again annealing the casting at a temperature of approximately 1450 F. for approximately three-quarters of an hour, and again cooling the casting.

9. The process of making malleable iron castings which includes casting an iron mixture which includes from 2.50% to 4.00% silicon, annealing the casting at a temperature in excess of 1750 F. for more than thirty minutes, aircooling the casting to a temperature not in excess of about 1200 F., again annealing the casting at a temperaturein excess of 1400 F.

for more than thirty minutes, and again cooling the casting.

10. The process of making malleable iron castings which includes casting an iron mixture which includes from 2.50% to 4.00% silicon, chilling the casting so rapidly that nearly all of the carbon is in the form of combined carbon, annealing the casting at a temperature in excess of 1750 F. for more than thirty minutes, air-cooling the casting to a temperature not in excess of about 1200 F., again annealing the casting at a temperature in excess of 1400 F. for more than thirty minutes, and again cooling the casting.

11. The process of making malleable iron castings which includes casting an iron mixture which includes from 2.50% to 4.00% silicon, annealing the casting at a temperature of approximately 1800" F. for approximately one hour, air-cooling the casting to a temperature not in excess of about 1200 F., again annealing the casting at a temperature of approximately 1450 F. for approximately three-quarters of an hour, and again cooling the casting.

12. The process of making malleable iron castings which includes casting an iron mixture which includes, from 2.50% to 4.00% silicon,

chilling the casting so rapidly that nearly all of the carbon is in the form of combined carbon, annealing the casting at a temperature of approximately 1800" F. for approximately one hour, air-cooling the casting to a temperature not in excess of about 1200 F., again annealing the casting at a temperature of approximately 1450 F. for approximately three-quarters of an hour, and again cooling the casting.

D. MOORE.